1. Field of the Invention
The invention relates to the field of apparatus and method for using light emitting diodes (LED) or other light sources to generate an efficient, narrow, high-aspect ratio beam.
2. Description of the Prior Art
The initial investment cost of LED illumination is very expensive when compared with traditional lighting means using the cost/lumen as the metric. While this may change over time, this high investment cost places a premium on collection and distribution efficiency of the LED optical system. The more efficient the system, the better the cost/benefit comparison with traditional illumination means, such as incandescent, fluorescent and neon.
A useful illumination device is the CCFL (cold cathode fluorescent lamp). This lamp is used in scanners, copiers, LCD computer monitors and fax machines as well as many other applications. Newly emerging in these devices is the use of multiple LEDs along a bar to simulate the CCFL.
However, the CCFL can require nearly 30 seconds of warm-up before it is stable enough to calibrate for operation. If LED could be used the devices would need no warm-up.
Utilizing a strip of closely spaced traditional LEDs, however, presents its own problem of thermal heat load due to the close proximity required to get a smooth light output. As the thermal load increases, LEDs will vary in their individual optical output response. This will cause the LED based system's calibration to change over time. This is a marked disadvantage for image quality in these devices.
The prior art in automotive CHMSL's is to use a strip of several LED's to generate a long, narrow output beam. The multiple LEDs may change in intensity as they age, resulting in a non-uniform device.
If a single LED could replace multiple LEDs in a device, cost could be reduced.
What is needed is an optical means to generate a narrow line of light which is not subject to the inherent disadvantages of such prior art.